<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<script>
    //1,递增和递减操作符。
    var age = 29;
    ++age;
    --age;
    //相当于var age= 29;age= age +1;
    //2,
    var num = 25;
    num = +num;//此处的num值并不会发生变化。
    console.log(num);
    //下面再进行大量的演示
    var s1 = '01';
    var s2 = '1.1';
    var s3 = 'z';
    var b = false;
    var f = 1.1;
    var o = {
        valueOf:function(){
            return -1;
        }
    };
    s1 = +s1;//1
    s2 = +s2;//1.1
    s3 = +s3;//NaN
    b = +b;//0
    f = +f;//1.1
    o = +o;//-1\

    s1 = -s1;//-1
    s2 = -s2;//-1.1
    s3 = -s3;//NaN
    b = -b;//0
    f = -f;//-1.1
    o = -o;//1\

</script>
</body>
</html>